The present invention relates to data recorder/reproducer head switching and preamplifying apparatus and, more particularly, to an electronic switching means for dual function record/playback heads, which means include a low noise, low input impedance preamplifier circuit in the playback path.
In certain types of tape recorder/reproducers wherein each transducing head serves for both the record and playback functions, it is necessary to provide switch means for switching each dual function head between a record path and a playback path in order to provide the corresponding recording and reproducing functions, respectively, via the same head. Typical of such recorder/reproducer apparatus is the DCRsi family of recorder/reproducers manufactured by Ampex Corporation, Redwood City, Calif.
In such tape recorders typically in present use, a preamplifier assembly located in the playback path includes the stator portion of a rotary transformer. The mating rotor portion of the transformer is part of an adjacent scanner assembly in which the dual function record/playback heads are located. The rotary transformer thus provides the electrical connection between the heads and a record driver amplifier in the record path, as well as between the heads and the preamplifier assembly in the playback path. Since each head serves both record and playback, the preamplifier assembly includes the switching means to connect each head either to a respective internal preamplifier assembly or to a respective record driver amplifier located in an adjacent assembly.
In the present state of the art, the switching function typically is done using mechanical relays. As long as the relays are working well they have the advantage of very low "on" resistance and very low "off" capacitance. These attributes, together with an inherent tolerance to high record signal voltages, and negligible contribution to playback noise, have been difficult to achieve in an electronic replacement for the mechanical relay. However, the mechanical relays have a poor contact reliability performance thus requiring excessive maintenance and replacement.
Accordingly, it would be highly desirable to provide an electronic switching means which not only exhibit the very low "on" resistance and "off" capacitance of the mechanical relays, but which also are directly interchangeable with existing mechanical relays without disturbing related circuit parameters such as, for example, the playback and record pilot phases.